a. the Z lines are pulled closer together
b. the I band remains the same
c. the A band becomes shorter
d. the H zone widens slightly
e. all of above

–what is the role of ATP in muscle contraction?
a. to form corss-bridges between thick and thin filaments
b.to break the cross-bridge when it binds to myosin and provide energy to myosin to form its high-energy configuration
c. to remove the tropomyosin-troponin complex from blocking the binding sites on actin
d. to bend the cross-bridge and pull the thin filaments toward the center of the sarcomere
e. to replace the supply of creatine phosphate

–how does calcium affect muscle contraction?
a. released from the T tubules
b. binding of acetylcholine opens calcium channels in the plasma membrane
c. binds to tropomyosin
d. causes tropomyosin to move away from the myosin-biding sites on the actin filament
e. release from sarcoplasmic reticulum changes the membrane potential of the muscle cell